Phase Changes and Phase Diagrams

• • Phase Changes are transformations of matter  from one physical state to another.
• PHASE DIAGRAMS is a graphical representation of the physical states  of a substance under different conditions of  temperature and pressure.
• It gives the possible combinations of pressure and  temperature at which a certain physical state or  states a substance would be observed: Phase Diagrams
• FEATURES OF PHASE DIAGRAMS

  1. Three Areas
  2. Three Lines
  3. Two Important Points (Triple Point and Critical Point)
• Three lines are the lines that serve as boundaries between  physical states represent the combinations of  pressures and temperatures at which two  phases can exist in equilibrium.
• Three areas are marked solid, liquid, and  vapor. Under a set of conditions in the  diagram, a substance can exist in a solid,  liquid, or vapor (gas) phase.
• The green line divides the solid and liquid  phases, and represents melting (solid to  liquid) and freezing (liquid to solid) points.
• • Melting (or freezing) curve 


  the curve on a  phase diagram which represents the  transition between liquid and solid states.
• • It shows the effect of pressure on the melting  point of the solid. Anywhere on this line,  there is equilibrium between the solid and the  liquid: Melting or Freezing Curve
• The blue line divides the liquid and gas  phases, and represents vaporization (liquid to  gas) and condensation (gas to liquid) points.
• The curve on a phase diagram which represents the transition between gaseous  and liquid states: Vaporization or Condensation curve
• The red line divides the solid and gas phases,  and represents sublimation (solid to gas) and  deposition (gas to solid) points.
• Sublimation or Deposition curve is the curve on a phase diagram which  represents the transition between gaseous  and solid states.
• The triple point is the combination of  pressure and temperature at which all three  phases of matter are at equilibrium.
• It is the point on a phase diagram at which  the three states of matter coexist: Triple Point
• The lines  that represent the conditions of solid-liquid,  liquid-vapor, and solid-vapor equilibrium  meet at the triple point.
• Two important Points: Critical Point and Triple Point
• The critical point terminates the liquid/gas  phase line.
• It is the set of temperature and  pressure on a phase diagram where the liquid  and gaseous phases of a substance merge  together into a single phase: Critical Point
• • Beyond the temperature of the critical point,  the merged single phase is known as a  supercritical fluid.